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raise AttributeError if loading fails in ctypes.LibraryLoader.__getattr__ #78997

lfriedri mannequin opened this issue Sep 27, 2018 · 7 comments

raise AttributeError if loading fails in ctypes.LibraryLoader.__getattr__ #78997

lfriedri mannequin opened this issue Sep 27, 2018 · 7 comments
3.8 only security fixes 3.9 only security fixes 3.10 only security fixes easy topic-ctypes type-bug An unexpected behavior, bug, or error


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lfriedri mannequin commented Sep 27, 2018

BPO 34816
Nosy @eryksun, @lfriedri, @farfella
  • gh-78997: AttributeError if loading fails in LibraryLoader.__getattr__ #25177
  • Files
  • 34816.patch
  • Note: these values reflect the state of the issue at the time it was migrated and might not reflect the current state.

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    GitHub fields:

    assignee = None
    closed_at = None
    created_at = <Date 2018-09-27.07:14:17.884>
    labels = ['easy', 'type-bug', '3.8', '3.9', '3.10', 'ctypes']
    title = 'raise AttributeError if loading fails in ctypes.LibraryLoader.__getattr__'
    updated_at = <Date 2021-04-04.02:29:42.566>
    user = '' fields:

    activity = <Date 2021-04-04.02:29:42.566>
    actor = 'ateeq'
    assignee = 'none'
    closed = False
    closed_date = None
    closer = None
    components = ['ctypes']
    creation = <Date 2018-09-27.07:14:17.884>
    creator = 'lfriedri'
    dependencies = []
    files = ['49932']
    hgrepos = []
    issue_num = 34816
    keywords = ['patch', 'easy']
    message_count = 5.0
    messages = ['326528', '326556', '326557', '389629', '390168']
    nosy_count = 3.0
    nosy_names = ['eryksun', 'lfriedri', 'ateeq']
    pr_nums = ['25177']
    priority = 'normal'
    resolution = None
    stage = 'patch review'
    status = 'open'
    superseder = None
    type = 'behavior'
    url = ''
    versions = ['Python 3.8', 'Python 3.9', 'Python 3.10']

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    Mannequin Author

    lfriedri mannequin commented Sep 27, 2018

    The following creates an OSError:

    import ctypes
    hasattr(ctypes.windll, 'test')

    The expected behavior would be to return "False"

    @lfriedri lfriedri mannequin added 3.7 (EOL) end of life topic-ctypes type-bug An unexpected behavior, bug, or error labels Sep 27, 2018
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    eryksun commented Sep 27, 2018

    ctypes.windll is an instance of ctypes.LibraryLoader, which has a __getattr__ method that calls ctypes.WinDLL(name) and caches the result as an instance attribute. I suppose with chained exceptions it's reasonable to handle OSError in __getattr__ by raising AttributeError. For example:

        class A:
            def __init__(self, name):
                raise OSError
        class B:
            def __getattr__(self, name):
                except OSError:
                    raise AttributeError


        >>> b = B()
        >>> b.test
        Traceback (most recent call last):
          File "<stdin>", line 4, in __getattr__
          File "<stdin>", line 3, in __init__
        During handling of the above exception, another exception occurred:
        Traceback (most recent call last):
          File "<stdin>", line 1, in <module>
          File "<stdin>", line 6, in __getattr__
        >>> hasattr(b, 'test')

    FYI, I recommend avoiding the cdll and windll LibraryLoader instances. I wish they were deprecated because globally caching CDLL and WinDLL instances leads to conflicts between projects that use the same shared libraries.

    @eryksun eryksun added the 3.8 only security fixes label Sep 27, 2018
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    Mannequin Author

    lfriedri mannequin commented Sep 27, 2018

    Thank you for your reply.

    I am not sure if I understood correctly:
    Do you suggest to modify so that the __getattr__ method of LibraryLoader catches the OSError and raises an AttributeError instead, as in your example?

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    eryksun commented Mar 28, 2021

    __getattr__ method of LibraryLoader catches the OSError and
    raises an AttributeError

    Yes. It seems no one was keen to work on this. I think it's relatively easy, so I'll add that flag in case someone is looking for an easy issue.

    @eryksun eryksun added easy 3.9 only security fixes 3.10 only security fixes and removed 3.7 (EOL) end of life labels Mar 28, 2021
    @eryksun eryksun changed the title ctypes + hasattr raise AttributeError if loading fails in ctypes.LibraryLoader.__getattr__ Mar 28, 2021
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    farfella mannequin commented Apr 4, 2021

    First patch fixing only the issue at hand on master. LibraryLoader now catches OSError for FileNotFoundError and raises AttributeError.

    @ezio-melotti ezio-melotti transferred this issue from another repository Apr 10, 2022
    FFY00 added a commit that referenced this issue Dec 15, 2022
    Co-authored-by: Zachary Ware <>
    Co-authored-by: Filipe Laíns <>
    Co-authored-by: Eric Wieser <>
    carljm added a commit to carljm/cpython that referenced this issue Dec 16, 2022
    * main:
      Improve stats presentation for calls. (pythonGH-100274)
      Better stats for `LOAD_ATTR` and `STORE_ATTR` (pythonGH-100295)
      pythongh-81057: Move the Cached Parser Dummy Name to _PyRuntimeState (python#100277)
      Document that zipfile's pwd parameter is a `bytes` object (python#100209)
      pythongh-99767: mark `PyTypeObject.tp_watched` as internal use only in table (python#100271)
      Fix typo in introduction.rst (python#100266)
      pythongh-78997: AttributeError if loading fails in LibraryLoader.__getattr__
      pythonGH-100234: Set a default value for random.expovariate() (pythonGH-100235)
      Remove uninformative itertools recipe (pythonGH-100253)
      pythonGH-99767: update PyTypeObject docs for type watchers (pythonGH-99928)
      Move stats for the method cache into the `Py_STAT` machinery (pythonGH-100255)
      pythonGH-100222: fix typo _py_set_opocde -> _py_set_opcode (pythonGH-100259)
      pythonGH-100000: Cleanup and polish various watchers code (pythonGH-99998)
      pythongh-90111: Minor Cleanup for Runtime-Global Objects (pythongh-100254)
    iritkatriel added a commit to iritkatriel/cpython that referenced this issue Dec 28, 2022
    * Correct CVE-2020-10735 documentation (python#100306)
    * pythongh-94912: Added marker for non-standard coroutine function detection (python#99247)
    This introduces a new decorator `@inspect.markcoroutinefunction`,
    which, applied to a sync function, makes it appear async to
    * Docs: Don't upload CI artifacts (python#100330)
    * pythongh-89727: Fix os.walk RecursionError on deep trees (python#99803)
    Use a stack to implement os.walk iteratively instead of recursively to
    avoid hitting recursion limits on deeply nested trees.
    * pythongh-69929: re docs: Add more specific definition of \w (python#92015)
    Co-authored-by: Jelle Zijlstra <>
    * pythongh-89051: Add ssl.OP_LEGACY_SERVER_CONNECT (python#93927)
    Co-authored-by: blurb-it[bot] <43283697+blurb-it[bot]>
    Co-authored-by: Christian Heimes <>
    Co-authored-by: Hugo van Kemenade <>
    Fixes python#89051
    * pythongh-88211: Change lower-case and upper-case to match recommendations in imaplib docs (python#99625)
    * pythongh-100348: Fix ref cycle in `asyncio._SelectorSocketTransport` with `_read_ready_cb` (python#100349)
    * pythongh-99925: Fix inconsistency in `json.dumps()` error messages (pythonGH-99926)
    * Clarify that every thread has its own default context in contextvars (python#99246)
    * pythongh-99576: Fix cookiejar file that was not truncated for some classes (pythonGH-99616)
    Co-authored-by: Łukasz Langa <>
    * pythongh-100188: Reduce misses in BINARY_SUBSCR_(LIST/TUPLE)_INT (python#100189)
    Don't specialize if the index is negative.
    * pythongh-99991: improve docs on str.encode and bytes.decode (python#100198)
    Co-authored-by: C.A.M. Gerlach <CAM.Gerlach@Gerlach.CAM>
    * pythongh-91081: Add note on WeakKeyDictionary behavior when deleting a replaced entry (python#91499)
    Co-authored-by: Pieter Eendebak <>
    Co-authored-by: Jelle Zijlstra <>
    * pythongh-85267: Improvements to inspect.signature __text_signature__ handling (python#98796)
    This makes a couple related changes to inspect.signature's behaviour
    when parsing a signature from `__text_signature__`.
    First, `inspect.signature` is documented as only raising ValueError or
    TypeError. However, in some cases, we could raise RuntimeError.  This PR
    changes that, thereby fixing python#83685.
    (Note that the new ValueErrors in RewriteSymbolics are caught and then
    reraised with a message)
    Second, `inspect.signature` could randomly drop parameters that it
    didn't understand (corresponding to `return None` in the `p` function).
    This is the core issue in python#85267. I think this is very surprising
    behaviour and it seems better to fail outright.
    Third, adding this new failure broke a couple tests. To fix them (and to
    e.g. allow `inspect.signature(select.epoll.register)` as in python#85267), I
    add constant folding of a couple binary operations to RewriteSymbolics.
    (There's some discussion of making signature expression evaluation
    arbitrary powerful in python#68155. I think that's out of scope. The
    additional constant folding here is pretty straightforward, useful, and
    not much of a slippery slope)
    Fourth, while python#85267 is incorrect about the cause of the issue, it turns
    out if you had consecutive newlines in __text_signature__, you'd get
    Finally, the `if name is invalid:` code path was dead, since
    `parse_name` never returned `invalid`.
    * pythonGH-100363: Speed up `asyncio.get_running_loop` (python#100364)
    * pythonGH-100133: fix `asyncio` subprocess losing `stderr` and `stdout` output (python#100154)
    * pythongh-100374: Fixed a bug in socket.getfqdn() (pythongh-100375)
    * pythongh-100129: Add tests for pickling all builtin types and functions (pythonGH-100142)
    * Remove unused variable from `dis._find_imports` (python#100396)
    * pythongh-78878: Fix crash when creating an instance of `_ctypes.CField` (python#14837)
    * pythonGH-69564: Clarify use of octal format of mode argument in help(os.chmod) (python#20621)
    Co-authored-by: Kumar Aditya <>
    * pythonGH-99554: Pack location tables more effectively (pythonGH-99556)
    * Correct typo in (python#100423)
    In the docstring of `ParamSpec`, the name of `P = ParamSpec('P')` was
    mistakenly written as `'T'`.
    * pythongh-99761: Add `_PyLong_IsPositiveSingleDigit` function to check for single digit integers  (python#100064)
    * pythonGH-99770: Make the correct call specialization fail kind show up in the stats (pythonGH-99771)
    * pythongh-78997: fix bad rebase of moved test file (python#100424)
    * pythongh-100344: Add C implementation for `asyncio.current_task` (python#100345)
    Co-authored-by: pranavtbhat
    * pythonGH-99554: Trim trailing whitespace (pythonGH-100435)
    Automerge-Triggered-By: GH:brandtbucher
    * pythongh-85432: Harmonise parameter names between C and pure-Python implementations of `datetime.time.strftime`, `datetime.datetime.fromtimestamp` (python#99993)
    * pythongh-57762: fix misleading tkinter.Tk docstring (python#98837)
    Mentioned as a desired change by terryjreedy on the corresponding issue,
    since Tk is not a subclass of Toplevel.
    * pythongh-48496: Added example and link to faq for UnboundLocalError in reference (python#93068)
    * Fix typo in 3.12 What's New (python#100449)
    * pythongh-76963: PEP3118 itemsize of an empty ctypes array should not be 0 (pythonGH-5576)
    The itemsize returned in a memoryview of a ctypes array is now computed from the item type, instead of dividing the total size by the length and assuming that the length is not zero.
    * pythonGH-100459: fix copy-paste errors in specialization stats (pythonGH-100460)
    * pythongh-99110: Initialize `frame->previous` in init_frame to fix segmentation fault when accessing `frame.f_back` (python#100182)
    * pythongh-98712: Clarify "readonly bytes-like object" semantics in C arg-parsing docs (python#98710)
    * pythongh-92216: improve performance of `hasattr` for type objects (pythonGH-99979)
    * pythongh-100288: Specialise LOAD_ATTR_METHOD for managed dictionaries (pythonGH-100289)
    * Revert "pythongh-100288: Specialise LOAD_ATTR_METHOD for managed dictionaries (pythonGH-100289)" (python#100468)
    This reverts commit c3c7848.
    * pythongh-94155: Reduce hash collisions for code objects (python#100183)
    * Uses a better hashing algorithm to get better dispersion and remove commutativity.
    * Incorporates `co_firstlineno`, `Py_SIZE(co)`, and bytecode instructions.
    * This is now the entire set of criteria used in `code_richcompare`, except for `_PyCode_ConstantKey` (which would incorporate the types of `co_consts` rather than just their values).
    * pythongh-83076: 3.8x speed improvement in (Async)Mock instantiation (python#100252)
    * pythongh-99482: remove `jython` compatibility parts from stdlib and tests (python#99484)
    * bpo-40447: accept all path-like objects in compileall.compile_file (python#19883)
    Signed-off-by: Filipe Laíns <>
    Signed-off-by: Filipe Laíns <>
    Co-authored-by: Irit Katriel <>
    Co-authored-by: Shantanu <>
    * pythonGH-100425: Improve accuracy of builtin sum() for float inputs (pythonGH-100426)
    * pythongh-68320, pythongh-88302 - Allow for private `pathlib.Path` subclassing (pythonGH-31691)
    Users may wish to define subclasses of `pathlib.Path` to add or modify
    existing methods. Before this change, attempting to instantiate a subclass
    raised an exception like:
        AttributeError: type object 'PPath' has no attribute '_flavour'
    Previously the `_flavour` attribute was assigned as follows:
        PurePath._flavour        = xxx not set!! xxx
        PurePosixPath._flavour   = _PosixFlavour()
        PureWindowsPath._flavour = _WindowsFlavour()
    This change replaces it with a `_pathmod` attribute, set as follows:
        PurePath._pathmod        = os.path
        PurePosixPath._pathmod   = posixpath
        PureWindowsPath._pathmod = ntpath
    Functionality from `_PosixFlavour` and `_WindowsFlavour` is moved into
    `PurePath` as underscored-prefixed classmethods. Flavours are removed.
    Co-authored-by: Alex Waygood <>
    Co-authored-by: Brett Cannon <>
    Co-authored-by: Adam Turner <>
    Co-authored-by: Eryk Sun <>
    * pythongh-99947: Ensure unreported errors are chained for SystemError during import (pythonGH-99946)
    * Add "strict" to dotproduct(). Add docstring. Factor-out common code. (pythonGH-100480)
    * pythongh-94808: improve test coverage of number formatting (python#99472)
    * pythongh-100454: Start running SSL tests with OpenSSL 3.1.0-beta1 (python#100456)
    * pythongh-100268: Add is_integer method to int (python#100439)
    This improves the lives of type annotation users of `float` - which type checkers implicitly treat as `int|float` because that is what most code actually wants. Before this change a `.is_integer()` method could not be assumed to exist on things annotated as `: float` due to the method not existing on both types.
    * pythongh-77771: Add enterabs example in sched (python#92716)
    Co-authored-by: Shantanu <>
    * pythonGH-91166: Implement zero copy writes for `SelectorSocketTransport` in asyncio (python#31871)
    Co-authored-by: Guido van Rossum <>
    * pythonGH-91166: Implement zero copy writes for `SelectorSocketTransport` in asyncio (python#31871)
    Co-authored-by: Guido van Rossum <>
    * Misc Itertools recipe tweaks (pythonGH-100493)
    * pythongh-100357: Convert several functions in `bltinsmodule` to AC (python#100358)
    * Remove wrong comment about `repr` in `test_unicode` (python#100495)
    * pythongh-99908: Tutorial: Modernize the 'data-record class' example (python#100499)
    Co-authored-by: Alex Waygood <>
    * pythongh-100474: Fix handling of dirs named index.html in http.server (pythonGH-100475)
    If you had a directory called index.html or index.htm within a directory, it would cause http.server to return a 404 Not Found error instead of the directory listing. This came about due to not checking that the index was a regular file.
    I have also added a test case for this situation.
    Automerge-Triggered-By: GH:merwok
    * pythongh-100287: Fix unittest.mock.seal with AsyncMock (python#100496)
    * pythongh-99535: Add test for inheritance of annotations and update documentation (python#99990)
    * pythongh-100428: Make float documentation more accurate (python#100437)
    Previously, the grammar did not accept `float("10")`.
    Also implement mdickinson's suggestion of removing the indirection.
    * [Minor PR] Quotes in documentation changed into code blocks (python#99536)
    Minor formatting fix in documentation
    Co-authored-by: Shantanu <>
    * pythongh-100472: Fix docs claim that compileall parameters could be bytes (python#100473)
    * pythongh-100519: simplification to `eff_request_host` in (python#99588)
    `IPV4_RE` includes a `.`, and the `.find(".") == -1` included here is already testing to make sure there's no dot, so this part of the expression is tautological. Instead use more modern `in` syntax to make it clear what the check is doing here. The simplified implementation more clearly matches the wording in RFC 2965.
    Co-authored-by: hauntsaninja <>
    * pythongh-99308: Clarify re docs for byte pattern group names (python#99311)
    * pythongh-92446: Improve argparse choices docs; revert bad change to lzma docs (python#94627)
    Based on the definition of the classes, it is more accurate to use "sequence" instead of "container" when describing argparse choices.
    A previous attempt at fixing this in python#92450 was mistaken; this PR reverts that change.
    Co-authored-by: Shantanu <>
    * Fix name of removed `inspect.Signature.from_builtin` method in 3.11.0a2 changelog (python#100525)
    * pythongh-100520: Fix `rst` markup in `configparser`  docstrings (python#100524)
    * pythongh-99509: Add `__class_getitem__` to `multiprocessing.queues.Queue` (python#99511)
    * pythongh-94603: micro optimize list.pop (pythongh-94604)
    * Remove `NoneType` redefinition from `` (python#100551)
    * pythongh-100553: Improve accuracy of sqlite3.Row iter test (python#100555)
    * pythonGH-98831: Modernize a ton of simpler instructions (python#100545)
    * load_const and load_fast aren't families for now
    * Don't decref unmoved names
    * Modernize GET_ANEXT
    * Modernize GET_AWAITABLE
    * Modernize ASYNC_GEN_WRAP
    * Modernize YIELD_VALUE
    * Modernize POP_EXCEPT (in more than one way)
    * Modernize PREP_RERAISE_STAR
    * Modernize LOAD_BUILD_CLASS
    * Modernize STORE_NAME
    * Modernize LOAD_NAME
    * Modernize LOAD_CLASSDEREF
    * Modernize LOAD_DEREF
    * Modernize STORE_DEREF
    * Modernize COPY_FREE_VARS (mark it as done)
    * Modernize LIST_TO_TUPLE
    * Modernize LIST_EXTEND
    * Modernize SET_UPDATE
    * Modernize DICT_UPDATE
    * Modernize DICT_MERGE
    * Modernize MAP_ADD
    * Modernize IS_OP
    * Modernize CONTAINS_OP
    * Modernize CHECK_EXC_MATCH
    * Modernize IMPORT_NAME
    * Modernize IMPORT_STAR
    * Modernize IMPORT_FROM
    * Modernize JUMP_FORWARD (mark it as done)
    * Modernize JUMP_BACKWARD (mark it as done)
    Signed-off-by: Filipe Laíns <>
    Signed-off-by: Filipe Laíns <>
    Co-authored-by: Jeremy Paige <>
    Co-authored-by: Carlton Gibson <>
    Co-authored-by: Hugo van Kemenade <>
    Co-authored-by: Jon Burdo <>
    Co-authored-by: Stanley <>
    Co-authored-by: Jelle Zijlstra <>
    Co-authored-by: Thomas Grainger <>
    Co-authored-by: Brad Wolfe <>
    Co-authored-by: Richard Kojedzinszky <>
    Co-authored-by: František Nesveda <>
    Co-authored-by: Pablo Galindo Salgado <>
    Co-authored-by: Nikita Sobolev <>
    Co-authored-by: Łukasz Langa <>
    Co-authored-by: Dennis Sweeney <>
    Co-authored-by: Bisola Olasehinde <>
    Co-authored-by: C.A.M. Gerlach <CAM.Gerlach@Gerlach.CAM>
    Co-authored-by: Pieter Eendebak <>
    Co-authored-by: Shantanu <>
    Co-authored-by: Kumar Aditya <>
    Co-authored-by: Dominic Socular <>
    Co-authored-by: Serhiy Storchaka <>
    Co-authored-by: Hai Shi <>
    Co-authored-by: amaajemyfren <>
    Co-authored-by: Brandt Bucher <>
    Co-authored-by: david-why <>
    Co-authored-by: Pieter Eendebak <>
    Co-authored-by: penguin_wwy <>
    Co-authored-by: Eli Schwartz <>
    Co-authored-by: Itamar Ostricher <>
    Co-authored-by: Alex Waygood <>
    Co-authored-by: Eric Wieser <>
    Co-authored-by: Irit Katriel <>
    Co-authored-by: Bill Fisher <>
    Co-authored-by: Petr Viktorin <>
    Co-authored-by: Ken Jin <>
    Co-authored-by: Carl Meyer <>
    Co-authored-by: Filipe Laíns <>
    Co-authored-by: Raymond Hettinger <>
    Co-authored-by: Barney Gale <>
    Co-authored-by: Brett Cannon <>
    Co-authored-by: Adam Turner <>
    Co-authored-by: Eryk Sun <>
    Co-authored-by: Sebastian Berg <>
    Co-authored-by: Illia Volochii <>
    Co-authored-by: JosephSBoyle <>
    Co-authored-by: James Frost <>
    Co-authored-by: MonadChains <>
    Co-authored-by: Bart Broere <>
    Co-authored-by: Glyph <>
    Co-authored-by: hauntsaninja <>
    Co-authored-by: Ilya Kulakov <>
    Co-authored-by: Guy Yagev <>
    Co-authored-by: Jakub Kuczys <>
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    Thanks, looks like this was fixed!

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    For the record, why was a backwards incompatible change made in just a point release without any deprecation warnings? We can work around this change from throwing OSError to AttrbteError in cdll but why on earth was this change added in a minor release?

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    3.8 only security fixes 3.9 only security fixes 3.10 only security fixes easy topic-ctypes type-bug An unexpected behavior, bug, or error
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